Palladium-Catalyzed Sequential Vinyl C–H Activation/Dual Decarboxylation: Regioselective Synthesis of Phenanthrenes and Cyclohepta[1,2,3-de]naphthalenes

Abstract

The application of a C(vinyl), C(aryl)-palladacycle from vinyl-containing substrates is challenging due to the interference of a reactive double bond in palladium catalysis. This Letter describes a [4 + 2] or [4 + 3] cyclization based on a C(vinyl), C(aryl)-palladacycle by employing α-oxocarboxylic acids as the insertion units under a palladium/air system. The reaction proceeded through the key vinyl C−H activation and dual decarboxylation sequence, forming phenanthrenes and cyclohepta[1,2,3de]naphthalenes regioselectively in good yields. The synthetic versatility of this protocol is highlighted by the gram-scale synthesis and synthesizing functional material molecule.

Decarboxylative cyclization of o-chlorobenzoic acids with C,C-palladacycles formed by an aminopalladation/dealkylation strategy to access dibenzo[a,c]carbazoles

“…On the basis of the above experimental results and previous work, 10–14,18 we propose a plausible mechanism for this protocol (Scheme 3). First, arylpalladium( ii ) species A is generated by oxidative addition of the C–Br bond in 1a to Pd(0), which is subsequently converted into intermediate B via an intramolecular aminopalladation by the coordination of Pd( ii ) to alkyne.…”

“…1 In the past few decades, five-membered C , C -palladacycle-based reactions have attracted widespread attention due to their versatile conversions in which two C–Pd bonds could be functionalized by trapping with coupling reagents. 2–16 Among them, of extraordinary interest to synthetic chemists are cyclizations of five-membered C , C -palladacycles with various coupling reagents such as aryl halides, 3 arynes, 4 alkynes, 5 diaziridinones, 6 diazo compounds, 7 bromophenols, 8 dibromomethane, 9 halogenated carboxylic acids, 10–14 etc ., which have emerged as a powerful tool for the construction of polycyclic compounds. Recently, the groups of Kwong, us and others achieved the transformation of five-membered C , C -palladacycles by various halogenated carboxylic acids via a carboxyl-assisted palladacycle capture strategy, leading to the construction of diverse fused polycycles (Scheme 1a).…”

“…Recently, the groups of Kwong, us and others achieved the transformation of five-membered C , C -palladacycles by various halogenated carboxylic acids via a carboxyl-assisted palladacycle capture strategy, leading to the construction of diverse fused polycycles (Scheme 1a). 10–14 Despite great progress, there are still some limitations in this field: (1) a C–H activation process was required to form C , C -palladacycles. (2) These methods were restricted to the construction of C–C bonds.…”

Research advances in palladium-catalysed intermolecular C–H annulation of aryl halides with various aromatic ring precursors

“…Subsequently, our group and others designed various halogenated carboxylic acids as C1, C2 or C3 insertion units to construct different size-ring fused cyclic compounds via this strategy. [53][54][55][56][57][58][59][60][61][62] In these reactions, it was observed that the inser- tion of carboxylic acids usually showed good regioselectivity. Thus, the methods used o-halobenzoic acids, arynes and aryl halides as aromatic ring precursors, which could be complementary.…”

“…Using BQ as a oxidant, Wu 54 developed a method for synthesizing phenanthrenes and cyclohepta[1,2,3-de]naphthalene using 2-iodophenylethylene and α-oxocarboxylic acids (Scheme 38). This method overcame the interference of a reactive double bond to form a C(aryl),C(aryl)-palladacycle through Organic & Biomolecular Chemistry Review vinyl C-H activation, and had special regioselectivity for nonsymmetrical PAHs.…”